The present invention pertains in general to anti-stalling systems and methods therefor for use with asymmetric, motor driven structures in the presence of wind pressure, and in particular to anti-stalling, rotating antenna buoy systems and methods therefor.
As a rotating antenna rotates in the presence of a directed movement of air, such as a wind, the wind exerts aerodynamic forces on the antenna. An asymmetrical rotating antenna is a rotating antenna for which the aerodynamic center of pressure of the antenna is different from the center of rotation of the antenna so that the antenna is subject to torsonal aerodynamic moments. Aerodynamic forces exerted by the wind on an asymmetrical antenna mounted on a mast can cause a rotational moment around the antenna mast that alternately helps or hinders the motion of the antenna as it rotates respectively into or away from the wind.
Placing a lage asymmetrical rotating antenna, such as a radar antenna, on a mast driven by a motor located within a small, streamlined buoy floating on water creates an additional problem. There is more resistance to rotation of the antenna in the wind than there is resistance to rotation of the buoy in the water. Therefore, it is the tendency of an asymmetrical rotating antenna which is erected on a buoy to remain stalled so that it presents the least amount of surface area to the wind while the buoy is driven to counter-rotate by the action of the motor therein.
A combined problem of a variable torque load applied to the motor because of alternately helpful or hindering wind moments and a counter rotational tendency on the part of the buoy make the implementation of a rotating antenna buoy system particularly difficult. The complexity, bulkiness and expense of such a system is increased by the need for rotational speed regulation equipment and a motor sufficiently large to overcome the peak values of the wind-induced moments.
One approach to compensating for wind effects on rotating antennas is to provide an over-all assisting torque to offset the wind-induced moments. This approach involves the use of a plurality of cups attached to one side an antenna or to some portion of an antenna supporting structure and oriented at angles so that the cups receive a greater force from the wind during one portion of a revolution than the remaining portion in order to aid rotation. Despite the beneficial effect on the varying torque load in the presence of the wind, this approach does not prevent the counter rotational problem present in rotating antenna buoy systems. Furthermore, such an approach is directed toward presenting a countervailing force at portions of the rotational cycle when wind-induced moments are greatest and not at reducing or distributing aerodynamic forces along the antenna. Thus, undesirable strain may result from the contest between the wind forces and the countervailing force. Furthermore, such a countervailing force approach does not lend itself well to cooperation with other anti-stalling devices except by increasing the complexity of the overall design.